Energy balance and body weight control are regulated by hypothalamic neurons through sensing nutrients; however, the underlying molecular basis is still much unclear. Hypoxia-inducible factor (HIF) has recently been known to be activated by normoxic metabolic signals, and our recent publication showed that hypothalamic HIF2?/HIF? responds to glucose and HIF knockout in hypothalamic neurons are obssogenic. Therefore, the objective of this research is to study hypothalamic nutrient-sensing mechanism and its importance in metabolic physiology or disease. Our recent preliminary studies further revealed that physiological levels of glucose or leucine both activated hypothalamic HIF2? to be causally associated with diet-induced metabolic responses. Hence, the hypothesis of this proposal is that hypothalamic HIF is important for diet-induced metabolic control in terms of appetite and energy expenditure (including the forms of diet-induced spontaneous physical activity and thermogenesis). This hypothesis leads to prediction that while hypothalamic HIF inhibition causes energy imbalance and obesity, hypothalamic HIF gene delivery can improve energy balance to counteract dietary obesity. Three Specific Aims are propsoed to: (1) study the effects of nutrients on hypothalamic HIF and the involved molecular mechanism; (2) study the effects of hypothalamic HIF manipulations in appetite and energy expenditure control (including diet-induced spontaneous physical activity and diet-induced thermogenesis), and also study the molecular mediators and the sympathetic nervous system-directed physiological mechanism; (3) study effects of hypothalamic HIF inhibition or activation on dietary obesity. Experimental approaches will be significantly based on analyses of metabolic and behavioral physiology as well as HIF pathway in normal mice and the models with hypothalamic HIF manipulations in relation with various nutrient deliveries. Success of this project can lead to a new paradigm of energy balance control and a new target for treating obesity.